and other tax proposals. >> president obama: governor romney was a very successful investor. if be somebody came to you with a plan that said, here, i want to spend 7- or $8 trillion, and we're going to pay for it, but we can't tell you until after the election how we're going to do it, you wouldn't have taken such a sketchy people, and neither should you, the american people, because the math doesn't add up. >> reporter: today we caught up with donald marin, an author of one of the analyses quoted by the president and others. >> governor romney has laid out four to five different principles in his tax reform. what our study concludes is it is not possible to accomplish all of them. if he is going to raise taxes on captain gains and businesses, it may be possible. but that's why we haven't seen one. >> reporter: for his part, governor romney says there are six studies that show he can fulfill his tax cut pledges. but while some of the analogies suggest that romney's plans might be plausible, under certain conditions not acknowledged by the governor, four are op-ed posts writt